Many types of solenoid valves are known in the prior art, particularly solenoid-actuated valves which fail in the closed condition. That is, when power to these valves is interrupted, the biasing means, which is usually a compression spring, forces an armature of the valve to move against a generally soft elastomeric sealing member such as a diaphragm or the like, in order to close the valve. While this configuration is highly beneficial in in many instances where serious leakage needs to be prevented, such as in a washing machine or an ice-maker, in some instances such a closed condition could be disastrous. That is, in some types of devices, providing a seal for an extended period of time could cause serious damage to the device as well as the environment surrounding the device.
A number of the above noted valves incorporate a diaphragm within a housing for providing a seal between an inlet and an outlet. With such valves, each stroke of the valve causes the diaphragm to be exercised which stresses the diaphragm. Over time, the continued exercising of the diaphragm will cause the diaphragm to rupture and fail. Also, oftentimes sediments in the fluid passing through the valve will collect on the diaphragm and hinder its proper operation.
U.S. Pat. No. 3,750,693 issued to Hardison discloses a valve for admitting ram air to an airplane fuel system. A popper element surrounds a stationary coil such that when the solenoid is energized, the poppet moves down to a closed position to close the valve and when the solenoid is de-energized, a spring moves the poppet to open the valve. However, this valve utilizes a balanced design such that pressures above and below the poppet are equalized. Moreover, the pressure within an inlet of the valve does not assist in maintaining the valve in the closed position, it is only the solenoid which maintains the valve closed. Further, in order for the valve to properly seal, a soft elastomeric seal is required, which over time will wear and become ineffective in sealing the valve when in the closed position. Also, it can be noted that the solenoid windings are subjected to the fluid medium passing through the valve. Consequently this valve would be ineffective in a system for handling liquids.
In an effort to overcome the above noted shortcomings, U.S. Pat. No. 4,733,697 issued to Baun discloses a system including a solenoid actuated pilot valve which utilizes a system pressure to open a primary valve. In the event that power to the solenoid of the pilot valve is interrupted, the primary valve will remain open assuring a flow of cooling water to rollers of a rolling mill. However, the pilot valve itself is a three-way valve and permits fluid flow when in the energized or de-energized condition albeit to two different flow paths.
Accordingly, there is a need in the marketplace for a solenoid actuated valve which will close only when an electrical signal is provided to the solenoid and will be normally open when the solenoid is de-energized either as part of the normal operation of the valve or as a result of an electrical failure in the system. Moreover, there is a need for a solenoid valve that would open under a broad range of input pressures, thereby permitting the valve to be utilized in a system where a variety of fluid pressures are passed through the valve or to enable a valve of lesser magnitude; that is, one having a smaller solenoid and weaker biasing means, thus reducing the overall cost of the valve.